| With the shortage of petroleum resources and environmental requirements, traditional chemical synthesis of papermaking additives more and more difficult to adapt to the requirements.So develop a new type of natural papermaking wet-end additives is imperative, and have attract attention of many researchers.Soy protein isolate is taking soy meal as raw material, obtained by low-temperature desolventizing product, and is a by-product from soybean industry。Soy protein isolate is a kind of natural and renewable, biodegradable polymer, with rich resources, low prices, and many other advantages. In order to be able to have the properties of papermaking retention and drainage aid required, cationic groups were grafted on the soy protein isolate by chemically modified to improve its surface charge and the modified soy protein isolate properties were systematically studied in the paper. Developing a new biodegradable polymer retention and drainage aid for the paper industry was expected.Firstly, the optimum conditions for synthesis of cationic soy protein isolate(CSPI) were discussed in this paper. And they were listed as the followings: 70℃ of reaction temperature, 4 h of reaction time, p H 10.0 of reaction system, 1:1.1 molar ratio of soy protein isolate(SPI) and cationic reagent(EPTA). The chemical structure and physical property of CSPI was analyzed by the techniques of FT-IR and TGA, respectively. The results revealed that EPTA was successfully grafted onto the amino groups of SPI. The thermal stability of CSPI was enabled them to be used as papermaking additives. In comparison with the controlled samples, the pulp drainage, fines retention and sheet strength of wet-end system with CSPI as additives had been highly enhanced. The microstructure of sheet was analyzed by SEM. It was found that the fiber bonding with CSPI additives was more closely. This result further proved that the strength ability of sheet with CSPI as additive could be can be greatly improved.Secondly, the collaborative effect of cationic soy protein isolate(CSPI) and carboxymethyl cellulose(CMC) as the strengthening agents in papermaking was studied in this study. The parameters, including adding order or molar ratio of CSPI and CMC, were controlled in order to evaluate the effect of this binary strengthening system on the physical properties of paper. It was found that the binary system with a 0.5:2.5 mass ratio of CMC to CSPI and an order of simultaneously addition had a better strengthening effect than that of CMC or CSPI single system. The pulp drainage and fines retention effects of paper using CMC/CSPI binary system as strengthening additives were better than those of CMC single system, but not as good as those of CSPI single system.Thirdly, the graft copolymers(CSPI-PEI) was prepared by a graft reaction between the free carboxylic acid groups of cationic soy protein isolate(CSPI) and the amino groups of polyethyleneimine(PEI) using 1-(3-(dimethylamino)propyl)-3-ethyl-carbodiimide hydrochloride(EDC) and N-hydroxysuccinimide(NHS) as the condensing agents. The chemical structure and physical property of CSPI-PEI was analyzed by the techniques of Laser particle size/Zeta potential,FT-IR,HPLC and PCD,respectively. The results revealed that EPTA and PEI were successfully grafted onto the side chain groups of SPI. Compared with SPI, the charge density and molecular weight of the graft copolymers were significantly improved, and the particle size of the grafts was also increased.The CSPI-PEI were used as papermaking additives in the papermaking wet-end system, the pulp drainage and fines retention also had been highly enhanced.Finally, Microparticle system was consisted of the best CSPI-PEI graft copolymer and Bentonite. The factors affecting the drainability and retention of deinked pulp of microparticle system, such as bentonite dosage, and p H were studied in this paper. It was found that shearing strength and conductivity have good effect on CSPI-PEI/ Bentonite Microparticle system compared to CSPI-PEI single system and has good retention and drainage effect in Medium alkaline. Furthermore, the microparticle system can also improve the physical properties of paper. |
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